Tractor-trailers are used for over the road transport of goods and other products. Typically, the trailer is pivotably connected to the tractor so that the combination can be maneuvered and with a spacing or “gap” between the tractor cab and the trailer. This gap is a particular source of drag for all tractor-trailers of all cross sectional shapes, including cylindrical tankers such as are used in the industrial gas bulk distribution business, the oil industry and etc.
Aerodynamic drag is a major contributor to fuel consumption, especially at speeds above 50 MPH. Aerodynamic improvements can contribute to fuel savings and provide cost reduction. Fuel consumption reduction also greatly enhances carbon footprint reduction and helps meet additional environmental quality standards and objectives. The gap described above adversely and significantly affects fuel economy. As will be discussed, reducing the size of this gap results in a reduction in fuel consumption of about seven percent.
Tractor-trailers in which a tank is mounted on the trailer are a particular type of bluff body vehicle known to have high drag coefficients. Aerodynamic drag in the gap area is known to be a function of the sub-optimal flow transition from the size and shape of the tractor cab and that of the trailer. The tanker trailer often has a frontal area with air impingement not otherwise deflected by the tractor cab. Also, with the nearly inevitable presence of side wind vectors, the enlarged gap due to the configuration of the tanker trailers allows entry of cross winds and associated forces which also act on the frontal face of the trailer. This resulting flow separation further contributes to increased aerodynamic drag and increased fuel consumption.
Where tractor-trailers are used for transport of liquefied atmospheric gases, these tankers often depart an air separation plant with the maximum over-the-road limited weight. This necessitates adjustments to the effective wheelbase for load distribution among the axles. This required redistribution of the weight tends to require further lengthening of the gap which in turn, additionally increases the aerodynamic drag in that spatial arrangement.
The reduction of drag by enclosing the gap between tractor and trailer with a gap fairing has been recognized in the prior art. In this regard, an example of a current commercially available gap fairing is described in U.S. Pat. No. 3,834,752 which discloses a gap fairing that is sized for the common range of gap distances, from the back plane of the tractor cab to the front plane and arc of swing of the box or van trailers, where the gap distance is markedly shorter than on fully loaded tanker trailers. More recently a gap fairing on an industrial gas bulk liquid delivery tanker has been introduced. This tractor included a “cab-over configuration”, still typically used in the United Kingdom and Europe but obsolete in the United States. The gap fairing for this recent design does not include an extended back portion required to optimally achieve maximum gap coverage. The gap fairing is attached to the tractor cab, resulting in the transmission of intended and possibly unintended loads into the very thin tractor cab surface necessitating supplemental structural enhancement. This particular fairing design would require significant modification, tooling, and fitting changes for use with a multitude of tractor sizes, shapes and materials of construction variability.
U.S. Patent Application No. 2011/0109121 discloses a gap fairing that can be used in connection with tractor-trailers having a tank that addresses the size and shape transition, from rectangular cab to cylindrical trailer, as well as consideration of the necessary spacing for tractor-trailer articulation during backing maneuvers. The fairing configuration attaches to the tractor cab, with the attendant imposition of loads on the cab surface and/or structure. This idealized shape, however, has been found by the inventors to represent a costly manufacturing challenge. In addition, the highly conformal fairing-to-cab interface would require significant changes to the design and tooling for a range of tractors with sizes, shapes or materials of construction variations.
As will be discussed the present invention provides a gap fairing for a tractor-trailer and the use of such a gap fairing in reducing drag. Among other advantages of a gap fairing in accordance with the present invention is that such gap fairing is attached directly to the tractor chassis independently of the cab, can be easily adapted for a variety of tractor-trailer designs and can be fabricated in a less expensive manner than gap fairings of the prior art.